Stabilizing means for cold cathode tube flip-flop circuits



Patented May 12, 1953 STABILIZING MEANS FOR COLD CATHODE TUBE FLIP-FLOP CIRCUITS Charles R. Williams, Hawthorne, and Glenn E.

Hagen, Aircraft, Inc., of California Lawndale, Calif., assignors to Northrop Hawthorne, Calif., a corporation Application August 18, 1950, Serial No. 180,257

Claims.

The present invention relates to cold cathode tube flip-flop circuits, and is an improvement on the circuit shown, described and claimed in a copending Hagen application, Serial No. 100,178, filed June 20, 1949.

' The term flip-flop, as used herein, defines a device which has two stable states and is capable of being triggered from one state to the other. A dual cold cathode gas tube flip-flop has two conducting stable states; either one cathode is conducting, or the other cathode is conducting. The tube is non-conducting only during relatively short transition times, and sufficient supply voltage is provided to insure reignition.

Circuits for use with dual cathode gas tubes to obtain flip-flop operations have the following elments in'common:

1. A supply voltage source higher than the firing voltage of the tube.

' 2. A current limiting resistance in series with the supply voltage.

3. A cathode circuit such that in either stable state the on cathode is at a higher positive potential than the off cathode.

4. A means of coupling in a triggering pulse which decreases the voltage across the tube and extinguishes the glow current.

5. A means of maintaining the on to off cathode differential voltage during the triggering transition time.

6. A means of delaying the rise of the voltage across the tube during triggering to allow ionization dissipation before refiring.

Flip-flop circuits having the above components are shown, described and claimed in the Hagen application cited above.

However, it has been found that when the anode of a dual cold cathode glow tube circuit of the type just above described is connected to the cathodes by a capacitance, oscillatory tendencies in the flip-flop circuit may develop.

To couple in a triggering pulse requires the use of coupling capacitors which connect the tube in series with a suitablepulse source. If this pulse source is of low internal resistance, then the effect of the coupling capacitor is to form an oscillatory circuit in the same manner as would be obtained by connecting a capacitor directly across the tube from anode to cathode. The use of resistance in series with the pulse source or of a high internal resistance source may be employed to damp out oscillation, but this method has the disadvantage that the input pulse is also attenuated by such resistance, thus requiring a source pulse of greater amplitude to trigger the flip-flop.

It is its very tendency to oscillate which makes the flip-flop tube susceptible to triggering. Hence, to a limited extent, it may be desirable to promote instability. With this object in view, it would be possible to connect a small capacitor directly across the tube provided the circuit had elsewhere sufiicient damping to prevent sustained oscillation. However, a capacitor so connected would shunt out and so attenuate the input pulse as to result in no gain in sensitivity of the flip-flop.

In accordance with the present invention, the use of crystal diodes in series with coupling or loading capacitors provides several advantages as follows:

1. Input pulses can be coupled into the tube relatively unattenuated by the series diode.

2. An additional parallel input, or a parallel capacitor-diode load across the tube does not shunt or attenuate the input pulse.

3. The rectifying action of the diode permits the coupling or loading capacitor to conduct current unimpeded in one direction only. In the present invention, the diode is usually connected to permit current flow through the capacitor upon increase in voltage across the tube, and to block when the tube voltage drops, such as when the tube refires. Thus, the capacitor is permitted to promote oscillation in one direction only, which is suificient to obtain high triggering sensitivity. Upon refiring, the blocking action of the diode prevents further oscillation.

4. A series crystal diode-capacitor load across the tube acts to damp out oscillation, whatever the source, because such oscillation immediately causes self bias to build up across the diode placing it in its high resistance state so that it absorbs oscillation energy.

It is an object of the present invention to provide a means of preventing oscillation in a dual cold cathode glow tube flip-flop circuit triggered by pulses from a pulse generator, and having a significant capacitance between the anode and the two cathodes.

It is another object of the present invention to provide a dual cold cathode glow tube flip-flop circuit having two stable states that can be triggered by input pulses from one state to the other but which is highly stable otherwise.

Briefly, the present invention involves the insertion of one or more rectifying diodes in any circuit capacitatively coupling the anode to the cathodes. The diode is particularly useful in the pulse input circuit. By the use of such rectifiers, the circuit can be readily operated at maximum sensitivity and speed without oscillation or loss of stability.

Our invention will be more fully understood by reference to the drawings in which:

Figure 1 is an elevational view of a preferred type of a dual cold cathode glow tube suitable for use in the circuit of the present invention.

Figures 2 to 7, inclusive, are diagrams showing various flip-flop circuit modifications embodying the present invention.

As shown in Figure l, the tube preferred for use in all of the circuits of Figures 2 to 7 is provided with an envelope l containing an anode wire 2, flanked on each side by a cathode wire 3 and 4. These wires pass through an external pinch 5 to form an anode lead 6 and cathode leads 7 and 8 respectively.

A preferred tube is one inch long by inch inside diameter. The gas pressure in the tube, and the anode to cathode spacing is adjusted to give a desirable firing to burning voltage differential. Electrode surface spacings of .030

inch in helium at 250 mm. Hg pressure are satisfactory, and cathode wires of .010 to .015 inch diameter, .1 inch long, will satisfactorily carry up to 1.0 ma. current. Suitable tube currents for flip-flop operation range from 0.1 to 1.0 ma. Such a tube will provide useable on to off cathode difierentials of from 50 to 150 volts. Burning voltages are about 150 to 209 volts and firing potentials are about 250 to 500 volts depending upon gas mixture, material, and condition of cathodes.

For long life and most dependable operation, we prefer that the tube have from one percent to five percent of a recombinable polyatomic gas therein, such as hydrogen or water vapor, for example, in addition to the inert gas filling, in accordance with the teachings of another copendin Hagen application, Serial No. 100,178, filed June 20, 1949. The anode area is not critical, and conduction usually occurs from relatively small area points on the anode surface. The anode is preferably placed centrally between the two cathodes to obtain symmetrical electrical characteristics and in the same plane with the cathodes for ease of manufacture. However, in the circuits of Figures 2, 3 and 4, the anode 2 is shown as entering the tube from the opposite end of the envelope from the cathodes, for ease of circuit illustration.

In the circuit of- Figure 2, anode 2 is connected to the positive end of a source through a limiting resistance ll. Each cathode is connected to the, negative end of source ll! through separate cathode resistances l2 and i3 respectively. Each cathode resistance is bridged by cathode capacitors i and. i respectively.

An input line 96 is connected to anode 2 at one end, and through an input capacitor ii and a rectifying diode Hi to a pulse generator 19 supplying negative pulses, to the input line. Diode it may be, for example, one of the crystal rectifier types well known in the art.

In the circuit of Figure 2, just above described, the resistance It is the current limiting resistance. Cathode resistances l2 and it create the differential cathode voltage which insures alternate cathode firing. Input capacitor l? serves the dual purpose of input coupling for negative input pulses, and of controlling the anode voltage rise' rate. The diode [8 passes negative pulses only to prevent oscillating tendencies that would be caused by connecting the input capacity directly across the anode and cathodes through the pulse generator. Cathode capacitors M and i5 are of suflicient size to maintain the cathode voltage differential during the transition time between the extinguishing ef the discharge to one cathode and the striking of the discharge to the other cathode. These capacitors i i and 15 also make the flip-flop more sensitive to the triggering pulses by reducing the impedance of the cathode circuit, and, hence, a greater portion of the input pulse will appear across the tube. The particular circuit shown in Figure 2 is limited in maximum speed of operation by the time constant of the RC circuits |2--l4 and i3l5.

The circuit of Figure 3 is the same as that of Figure 2 except that cathode capacitors I4 and iii are replaced by a single capacitor 28 connected directly across the cathodes 3 and Al for economy of components and space.

This circuit of Figure 3 is less sensitive to triggering pulses than the circuit of Figure. 2. because of the attenuation. of the pulses by resistances i2 and it, but for the most stable opera tion, still requires the use of the rectifier P8 in the input circuit.

The circuit of Figure 4 is the same as that of Figure 2, except that neon glow lamps 2! and 22 are connected across the respective cathode resistances. i2 and it. These lamps act both as visual indicators and as voltage regulators for the circuit. Rectifier is again cifectively stabilizes the circuit.

The circuit of Figure 5 is the same as that of Figure 3 except that cathode rectifiers 24 and 25 are connected respectively between cathodes 3 and i and their respective resistances l2 and 33. These latter rectifiers block the discharge of capacitor 25] during the transition time when the tube is non-conducting. Thus, the inter-cathode capacitor it can be made relatively small, and the time constant of the RC circuits l"2ii and i32 can be made relatively small. High operating rates up to 10 kc. have been obtained with this circuit with complete stability due to the use of the input rectifier i 8. This latter rectifier is also important in this circuit because when the circuit is loaded by the use of an output circuit across the anode and a cathode, this circuit will also introduce a capacitance across anode and cathodes, thus enhancing any tendency to oscillate.

The circuit of Figure 6 is the same as that of Figure 2 with an input circuit modification. Here a separate capacitor 25 is connected across anode and the two cathodes to control the rate of anode voltage rise. A. rectifier Illa is placed in series with capacitor 25 to prevent oscillation, and also to prevent attenuation of the input pulse.

The circuit of Figure '7 is shown only to demonstrate that the input pulses can be applied to all of the circuits, previously described, at the junction of the two cathode resistors 12 and [3 by transferring the limiting resistor I I, there designated as Ila, to the cathode side of source Ill. The circuit shown in Figure 7 is the same as that of Figure 3 except that the input line I5 is connected to the junction of cathode resistances-l2 and I3, and limiting resistance Ha is connected to the negative side of source It, the positive side of source, In being then connected directly to anode 2. In this. case, pulse generator I9 supplies positive pulses, and rectifier [8b is reversed to pass. these pulses.

Thus, in all of the circuits described above, input rectifiers i8, l8a and lb stabilize the circuit by preventing oscillation thereof by capacitance connected across the anode and the cathodes of the tube.

From the above description it will be apparent that there is thus provided a device of the character described possessing the particular features of advantage before enumerated as desirable, but which obviously is susceptible of modification in its form, proportions, detail construction and arrangement of parts without departing from the principle involved or sacrificing any of its advantages.

While in order to comply with the statute, the invention has been described in language more or less specific as to structural features, it is to be understood that the invention is not limited to the specific features shown, but that the means and construction herein disclosed comprise the preferred form of several modes of putting the invention into effect, and the invention is, therefore, claimed in any of its forms or modifications within the legitimate and valid scope of the appended claims.

What is claimed is:

1. A glow tube switch comprising an envelope, containing a filling of gas at glow discharge pressure, an anode element in said envelope, a lead for said anode element, two cold cathode elements in said envelope adjacent said anode, first cathode resistance means connected at one end to a cathode, second cathode resistance means connected at one end to the other cathode, the other ends of said cathode resistance means being connected together to form a cathode lead, limiting resistance means directly connected to one of said leads, a potential source connected to the other of said leads, said limiting resistance means and said source being connected together in series to place said anode at a positive potential, capacity means connected between said cathode elements to hold said cathodes at a differential potential after a discharge between one cathode element and said anode element, a pulse input line connected to the lead to which said limiting resistance means is directly connected, and a rectifying element in said input line passing energy substantially only in the input direction.

2. In a dual cold cathode single anode glow tube flip-flop circuit wherein a glow discharge is flipped from one cathode to the other by an input pulse applied to said anode, a pulse generator connected between said anode and both of said cathodes, a capacity in series with said pulse generator, and means for preventing other than the pulses generated by said pulse generator from being applied across said anode and said cathodes.

3. In a dual cold cathode single anode glow tube flip-flop circuit wherein a glow discharge is flipped from one cathode to the other by an input pulse applied to said anode, a pulse generator connected between said anode and both of said cathodes, a capacity in series with said pulse generator, and a rectifier in series with said pulse generator and said capacity and oriented to pass only said input pulses to said anode.

4. A stable cold cathode flip-flop circuit comprising a gas filled cold cathode tube having two cathodes and an anode, a voltage supply higher than the firing voltage of said tube, a current limiting resistance in series with said voltage supply, means for maintaining an on cathode at a higher potential than an oil cathode, a source of triggering input pulses connected across said anode and both of said cathodes, said pulses being of sufficient magnitude and of proper sign to extinguish an on cathode, a capacity in series with said source of input pulses, means for maintaining the on and off differential voltage during a triggering transition time, and a rectifier positioned across said anode and said cathodes and oriented to reduce the tendency of said tube to oscillate due to the capacity between said anode and said cathodes.

5. A stable cold cathode flip-flop circuit comprising a gas filled cold cathode tube having two cathodes and an anode, a voltage supply higher than the firing voltage of said tube, a current limiting resistance in series with said voltage supply, means for maintaining an on cathode at a higher potential than an off cathode, a source of triggering input pulses connected across said anode and both of said cathodes, said pulses being of suficient magnitude and of roper sign to extinguish an on cathode, a capacity in series with said source of input pulses, means for maintaining the on and off differential voltage during a triggering transition time, and a rectifier positioned across said anode and. said cathodes and oriented to reduce the tendency of said tube to oscillate due to the capacity between said anode and said cathodes, said rectifier being positioned in series with said pulse generator and said capacity.

CHARLES R. WILLIAMS. GLENN E. I-IAGEN.

References Cited in the file of this patent UNITED STATES PATENTS Number 

